Bottom Line:
However, uptake mechanisms remain rather poorly understood, and protocols always require optimization of transfection parameters.The results show that for all delivery modalities the cellular antisense activity increases (less than proportionally) with increasing volume (in some cases accompanied with increased toxicity), and that this effect is more pronounced at higher cell densities.These results emphasize that transfection efficacy using cationic carriers is critically dependent on parameters such as transfection volume and cell density, and that these must be taken into account when comparing different delivery regimes.

Affiliation: Department of Cellular and Molecular Medicine, Faculty of Health Sciences, The Panum Institute, University of Copenhagen, Copenhagen, Denmark.

ABSTRACTEfficient intracellular delivery is essential for high activity of nucleic acids based therapeutics, including antisense agents. Several strategies have been developed and practically all rely on auxiliary transfection reagents such as cationic lipids, cationic polymers and cell penetrating peptides as complexing agents and carriers of the nucleic acids. However, uptake mechanisms remain rather poorly understood, and protocols always require optimization of transfection parameters. Considering that cationic transfection complexes bind to and thus may up-concentrate on the cell surface, we have now quantitatively compared the cellular activity (in the pLuc705 HeLa cell splice correction system) of PNA antisense oligomers using lipoplex delivery of cholesterol- and bisphosphonate-PNA conjugates, polyplex delivery via a PNA-polyethyleneimine conjugate and CPP delivery via a PNA-octaarginine conjugate upon varying the cell culture transfection volume (and cell density) at fixed PNA concentration. The results show that for all delivery modalities the cellular antisense activity increases (less than proportionally) with increasing volume (in some cases accompanied with increased toxicity), and that this effect is more pronounced at higher cell densities. These results emphasize that transfection efficacy using cationic carriers is critically dependent on parameters such as transfection volume and cell density, and that these must be taken into account when comparing different delivery regimes.

Figure 4: Figure 4. Relative cellular luciferase antisense activity of PNA conjugated to PEI [PEI25K-(PEG8-SS-PNA)15]. HeLa pLuc705 cells were trypsinized and seeded in a 96 well plate at different cell numbers the day before transfection. Cells were treated with different volumes (50 µl/well for a relative volume 1) of the transfection solutions for 24 h: (A) 1 µM or (B) 2 µM PNA (PDP:PNA; 1:1). Cell samples were then subjected to luciferase analysis and cellular viability test. All tests were performed in triplicate and the results are given as average values ± standard error of the mean (SEM). Luciferase activity was analyzed using Bright-Glo reagent (Promega), normalized to cell viability (Figs. S1–5) and given as relative light units (RLU/cell).

Mentions:
Finally, we studied the volume-effect for a PNA-polyplex using a disulfide coupled PNA-PEI (polyethyleneimine) conjugate.8 A 4-fold antisense activity increase at 5 relative volumes was seen for both of the analyzed doses (1 and 2 µM), but in contrast to the other PNA conjugates, the transfection volume-effect for the PEI-PNA is not dependent on the PNA dose (at 1 and 2 µM), and showed a close to proportional dependence on the volume up to 4 relative volumes (Fig. 4), whereas only minor effect of the cell number was observed. Finally, the PNA-polyplexes exhibited a pronounced volume-dependent cellular toxicity at the lower cell densities (4 and 8 × 103 cells/well) and the higher concentration (2 µM) (Fig. S4).

Figure 4: Figure 4. Relative cellular luciferase antisense activity of PNA conjugated to PEI [PEI25K-(PEG8-SS-PNA)15]. HeLa pLuc705 cells were trypsinized and seeded in a 96 well plate at different cell numbers the day before transfection. Cells were treated with different volumes (50 µl/well for a relative volume 1) of the transfection solutions for 24 h: (A) 1 µM or (B) 2 µM PNA (PDP:PNA; 1:1). Cell samples were then subjected to luciferase analysis and cellular viability test. All tests were performed in triplicate and the results are given as average values ± standard error of the mean (SEM). Luciferase activity was analyzed using Bright-Glo reagent (Promega), normalized to cell viability (Figs. S1–5) and given as relative light units (RLU/cell).

Mentions:
Finally, we studied the volume-effect for a PNA-polyplex using a disulfide coupled PNA-PEI (polyethyleneimine) conjugate.8 A 4-fold antisense activity increase at 5 relative volumes was seen for both of the analyzed doses (1 and 2 µM), but in contrast to the other PNA conjugates, the transfection volume-effect for the PEI-PNA is not dependent on the PNA dose (at 1 and 2 µM), and showed a close to proportional dependence on the volume up to 4 relative volumes (Fig. 4), whereas only minor effect of the cell number was observed. Finally, the PNA-polyplexes exhibited a pronounced volume-dependent cellular toxicity at the lower cell densities (4 and 8 × 103 cells/well) and the higher concentration (2 µM) (Fig. S4).

Bottom Line:
However, uptake mechanisms remain rather poorly understood, and protocols always require optimization of transfection parameters.The results show that for all delivery modalities the cellular antisense activity increases (less than proportionally) with increasing volume (in some cases accompanied with increased toxicity), and that this effect is more pronounced at higher cell densities.These results emphasize that transfection efficacy using cationic carriers is critically dependent on parameters such as transfection volume and cell density, and that these must be taken into account when comparing different delivery regimes.

Affiliation:
Department of Cellular and Molecular Medicine, Faculty of Health Sciences, The Panum Institute, University of Copenhagen, Copenhagen, Denmark.

ABSTRACTEfficient intracellular delivery is essential for high activity of nucleic acids based therapeutics, including antisense agents. Several strategies have been developed and practically all rely on auxiliary transfection reagents such as cationic lipids, cationic polymers and cell penetrating peptides as complexing agents and carriers of the nucleic acids. However, uptake mechanisms remain rather poorly understood, and protocols always require optimization of transfection parameters. Considering that cationic transfection complexes bind to and thus may up-concentrate on the cell surface, we have now quantitatively compared the cellular activity (in the pLuc705 HeLa cell splice correction system) of PNA antisense oligomers using lipoplex delivery of cholesterol- and bisphosphonate-PNA conjugates, polyplex delivery via a PNA-polyethyleneimine conjugate and CPP delivery via a PNA-octaarginine conjugate upon varying the cell culture transfection volume (and cell density) at fixed PNA concentration. The results show that for all delivery modalities the cellular antisense activity increases (less than proportionally) with increasing volume (in some cases accompanied with increased toxicity), and that this effect is more pronounced at higher cell densities. These results emphasize that transfection efficacy using cationic carriers is critically dependent on parameters such as transfection volume and cell density, and that these must be taken into account when comparing different delivery regimes.